Advanced Electrolyte Formula for Robust Operation of Vanadium Redox Flow Batteries at Elevated Temperatures

Insufficient thermal stability of vanadium redox flow battery (VRFB) electrolytes at elevated temperatures (>40 °C) remains a challenge in the development and commercialization of this technology, which otherwise presents a broad range of technological advantages for the long-term storage of intermittent renewable energy. Herein, a new concept of combined additives is presented, which significantly increases thermal stability of the battery, enabling safe operation to the highest temperature (50 °C) tested to date. This is achieved by combining two chemically distinct additives—inorganic ammonium phosphate and polyvinylpyrrolidone (PVP) surfactant, which collectively decelerate both protonation and agglomeration of the oxo-vanadium species in solution and thereby significantly suppress detrimental formation of precipitates. Specifically, the precipitation rate is reduced by nearly 75% under static conditions at 50° C. This improvement is reflected in the robust operation of a complete VRFB device for over 300 h of continuous operation at 50 °C, achieving an impressive 83% voltage efficiency at 100 mA cm^‒2 current density, with no precipitation detected in either the electrode/flow-frame or electrolyte tank.